Multdyocal lens and method of



Aug. 11, 1936. I G. A. CLEME NT Re. 20,059

MUIPTIFOCAL LENS AND METHOD MAKING SAME Original Filed May 13, 1932 ATTORNEY- Reissued .Aug. 11, 1936,

UNITED STATES PATENT OFFICE" George A. Clement, Mount Vernon, N. Y.

Original No. 1,911,806, dated May 30, 1933, Serial No. 611,035, May 13, 1932. Application for reissue November 17, 1933, Serial No. 698,527

17 Claims. (Cl. 8H4) My invention relates to fused multifocal lenses Another characteristic of my invention is the and blanks therefor, i. e., blanks having a minor provision of laterally extending marks on oppolens of one index of refraction fused in a desite sides of the segment to guide one in grindpnession or countersink in a major lens of difiert a k 50 as to enable him to throw, the ent index of refraction. Both bifocal and tricenter of the segment: in or out the desired focal lenses are thus made, but for the purpose of amount. In a button having the two-part collar this disclosure the discussion will be confined to of crown glass surrounding the flint segment these m bifocals. lines are formed by the proximate edges of the In spectacle lenses of this type the minor lens two parts of the collar. If a space is left between is of the higher index to form the reading segse edges, the a ce t s oul e s S ve to form ment. Quite commonly the major lens constitutthe guide marks, while if the two sections have ing the distance vision portion is of crown glass their proximate edges fused together, the line of n and the reading segment for near vision is of fusion remains visible and'forms the index marks.

flint glass. The depression is usually ground in It has been observed that the shouldered pethe convex side of meniscus blanks and is itriphery of the segment in the finished lens forms 15 self either spherical or piano, for the higher a bright band which is objectionably noticeable. powers of addition being a concave countersink. My invention comprehends means for eliminating If the minor lens blankbe one homogeneous piece the bright character of this e s w l b of glass of a single index throughout, as for exe fte f y desellbedample, a, flint button, when the bifocal r c v x I shall now explain my invention with reference side of the blank is finally surfaced, the inserted to e a mp nyin r win an sh ll thereafter button becomes a spherical wafer with a thin, point out my inve t on in claimsknife edge periphery. The optical center of such, F ur 1 i a f view of the thr e elements a'segment is substantially at its geometrical cenc posing t e utt comprehended y y nter when the opposite face of the blank is finished t-i S O t button in an intermediate 25 to prescription, and furthermore in the higher Stage 0 P duction reading powers the color at the edges of the seggu e 2 is a vertical central cross section of ment due to chromatic aberration becomes s troublesome, Figure 3 is a face view of the same in completed To raise the optical center'of the-segment and Condition 30 to give the segment a shouldered periphery m- Figure 4 is a face view of the bifocal side of the stead of a knife edge and thus avoid the colors p e e b a k after he but on is u d n the of the edge, the minor lens blank or button may countersink. be made with a flint or other high index center Figure 5 is eentlfll sectional elevation of the surrounded by crown glasspr glass of the index same 011 the line H 0! 35- of the major blank, the flint and the surrounding u e 6 is trensveme Beetlenll Dllln 0f the crown glass being edge fused together; and it is Same on the line 6-6 of Fig. 4. n T to blanks and lenses of this character. that my. Figures '7, 8 and 9 are successive views of the invention particularly pertains. bifocal face of the blank in successivestages of One of the principal advantages of my invengrinding. 40

tion is the elimination of thedanger of breakage Figure 10 is a view of the bifoeal face of a in the fusing of the button due to the unequal blank having the button fused in the counter.- expansion and contraction of the two kinds of sink, the'button having a slight space between glass. Another advantage is the provision of the proximate edges of the two surrounding or guide marks on opposite sides of the segment to collar sections. a 4Q serve as indices to the grinder'in the lateral dis- Figure 11 shows the bifocal face, of the same position of the optical center of the segment, that blank in finished form. I is, in disposing the center in or out as desired. Figure 12 is a detail in perspective. of the but- Otherobjects and advantages of my invention ton shown in Fig. 10, prior to fusing and with the '50 will appear from the following description. three elements separated.

One characteristic of my invention is the fact In discussing my invention I shall refer to the that the collar of the button member which is glass of the major'lens blank and of the collar edge fused about the flint segment is in two parts, portion of the button surrounding the segment 7 and the parts are so fltted and fused togethed as as crown glass, and I shall refer to the'glass of 65 toeliminatethe danger of breakageduring fusing. the segment itself as flint glass, it being understood that these are notintended to be'used in any limiting sense, the only requisite being that the segment shall have a different index of refractionfrom the collar and that the index of the collar be substantially that of the major blank portion in bifocal lenses.

In the finished button, as shown in Fig.3, the flint segment A is surrounded by two collar sections B and C, edge fused thereto and to each other. One mode of procedure in the making of this button is suggested in Figs. 1 and 2. The

segment A can be made of any desired shape. In this illustrated form it approximates a semicircle with its upper edge slightly curveddownwardly. First the flint segment A canbe ground to semicircular form, as shown in Figure 1, and the collar section B have one edge concaved to receive and fit about the circular edge ofthe segment. Thetwo may then be fused together, as shown in Figs. 1 and 2,-and the top edge may then be ground oifto a continuous downward curvature, as indicated by the dotted line. The collar section C may have one edge ground to the same curvature as the top edge of the other two elements, after which section C will be fitted and fusedin place, as shown in Fig. 3. This process of forming the button minimizes the danger of breakage due to the-unequal expansion of the flint and crown glass and at the same time the fusion of the proximate edges of the sections 13 and together provides the demarcation lines D and b', which serve as guides in the subsequent grinding ofthe bifocal face, as will hereinafter more fully appear.

This composite buttofi is larger than the usual flint button used in the manufacture of Kryptok lenses. Consequently the depression or countersink which is ground in the edge of the blank is correspondingly larger.

1 This is illustrated in Figs. 4, 5 and 6, where the composite button is shown as fused in the I spherical countersink formed in the convex face of the meniscus blank D. This fusing is afamiliar operation and need not be described further than to say that the one face of the button is ground substantially with.

thereof, the segment 4 alone remaig distinguishable by reason refraction. I I 4 The blank is finished by grinding the bifocal surface down to a continuous base curvature and polishing or surface finishing it, the blank being usually'sold from the factory in that form, that of its diflerent index of is, flnishedon one side, the other side being ground and finished by the dispenser in accordance with the prescription.

In the rough stage, that is, after fusing and before the bifocal face is ground down andfinished, the segment A-has a shouldered edge around its entire periphery. The 'disposition of theoptical center of the segment, which is. in-

depend upon the axis of generation of the finished bifocal surface. If, for example, the bifocal surfacebeflnishedtoth'at indicated by the dotted linemarkedBSinFigs.5and6,it willbeobserved that the optical center of the reading segment will be well above and considerably to the left of the geometrical center. -That is bethe button is the one first ground and that angula'r dispodtion of the blank is maintained cause the flint segment as thus ground is a decided prism with the base up and out, the reeds ing segment being for that reason decentered toward the prism base.

This moving of the center out or to the left is made possible by reason of the index lines b and b, as appears in Figs. '1, 8 and 9. The flrstor rough grinding of the bifocal side of the blank is as a rule done by hand, that is, the grinder holds the blank with the bifocal side against a revolving lap of a predetermined base curvature. If it is desired to throw the center in, as represented in Fig. 6, the blank will be presented atan angle to the lap so as to grind off the right side of the button, as viewed in Figs. 5 and 6, faster than the left side; also to throw the center up the blank is so presented to the lap as to grind the bottom of the button faster than the top. In other words, the lower righthand quadrant of throughout the subsequent grinding until the surface is finished.

The amount which the center is thrown in or out canbe very accurately gaged by the relative lengths of'the index lines-b and b, and as far as I I am' aware this is the first fused blank which deeenter it that amount toward the temple side of the lens, and let it be assumed that the lines- 'b and b are each four millimeters in length. The operator will present the blank to the rotating lap with the lower righthand quadrant in contact therewith and what in his, judgment is appronmately the right inclination. In order to' deeenter the segment one millimeter to the left, it is necessary that the grinding be'so started that two millimeters of the line b be ground off before the line b begins to shorten in the grinding operation. condition is substantially illustrated in Fig. 7. The continued grinding of the button with the blank presented at this angle further shortens the line b and begins to shorten the line b at the same rate. This is substantially illustrated in Fig. 8, where the shoulder of the collar or outer periphery of the button has been ground away in the lower righthand quadrant. The grinding of the surface at this same angle will be continued until the shoulder of the 3 button and' the exposed portion of the countersink has been entirely ground away. This conknows that the center is substantially raised.

the geometrical center of the t. After the opposite side of the blank is ground to sired shape, for example, that indicated by the dottedseircular line in Fig. 9, which, aswill be observed, leavesa portion of the distance lens below the reading segment, for aid in loofi'ng down, as for example, in descending steps.

Instead of fusing the button in the two operations, as above described, and actually bringing the sections B and C into physical union, a small space may be left between the proximate edges of the two sections and the three elements 75' prescription the lens will be cut out to the de- V the shape of'the segment in Fig. 11.

befusedtogetherinasinglefusing operati Such a button is illustrated in .Fig. 10. In this casethesegmentAwili initiallybe'groundtoits final shape and the'collar sections of crown glass B and C will be shaped to fit exactly about their rupective portion of the segment, the edges of the opposing lateral portions of the collar sections being ground so as to leavepreferably a very slight clearance to insure exact'fitting of the collar sections about the segment. This clearance need not be more than a fraction of a millimeter. and is shown somewhat exaggerated in Fig. 10. However, since this clearance leaves two spaced shoulders instead of a line of fusion it is necessary in the final grinding that the shoulders be entirely ground away. The shoulders do, however, form lateral demarcations which will guide the grinder in throwing the center of the segment in or out, as desired.

In Fig. 10 the dotted circular line It indicates the outline of the recessor depression in one finished position of the bifocal surface.

Figure 11 represents the bifocal side of the blank finishedso as to have the recess R dis-' posed as indicated in Fig. 10. In such case the optical center of the segment is substantially at the point x. Laterally the recess R is symmetrically disposed with respect to the segment A and in order to assure the complete elimination of the shoulders of the proximate edgesof the col-- lar sections 2Bv and C, thegrinding is continued, as indicated by the circle R, until it enters the corners of the segment. Theresult is shown by To throw the center a: in or out it is only necessary to so dispose the finished bifocal surface that the recess R is disposed laterally and eccentric to the segment in the direction that it is desired to throw the center. The extent of the lateral shifting of the recess R with respect to the segment will be controlled and guided by the shoulders as indices. When the center is thus laterally shifted with this type of button, the finished segment will be asymmetrical in that one corner will be ground'off to a greater extent than the other. This, however,',will scarcely be observable to the ordinary wearer and will be of little or no disadvantage.

Bince the segment in this type of lens is boundedby a shoulder rather than by a knife edge, that shoulder serves to diffuse and reflect the light and presents a band in the finished lens, which at times is obiectionably bright. In order to obvi'ate this I propose to treat this shoulder in such a way as to make it substantially opaque and non-reflective. For this purpose I apply between the edges of the collar and of the segment a film which will serve as a light screen and yet will not interfere with the molecular union of the ad- 'iacent surfaces, in other words, at the fusing heat will have an afiinlty for the glam.

Many substances can be used for such film but mixed with-any one of several of the, common fluxes used in ceramics. Among suitable fluxes for this purpose may bementioned lead oxide. boric acid, soda, potash-barium, alumina, lime and magnesia. A combination of such fluxes, such as soda, lime and magnesia, together with a suitable dye, provides a very satisfactory light screenwhenapplied asafilm tothe glassshoulders prior to fusing. For example, as indicated in Fig. 12, the material may be applied as a film to the edge of the'segment A before the parts are fittedtogetherandi'used. Inthisfigurethethrce elements of the button are shown separated butreadytobefittedtogethertoproduceabutton. similar to the one shown in Fig. 10.

Other embodiments of my invention than those above mentioned will readily occur to those skilled 5 in the art. For example, lines of demarcation. such as b and b, may be produced optionally on one or the-other of the contact fusing surfaces. when the lines are not produced by the fusing of the button. In such case the index lines may be 10 marked at opposite points either on the fusing surface of the collar or of the countersink.

I claim: i. A multiiocal lens blank comprising a major lens portion of one index of refraction having a 15 countersink in one face thereof. and a minor lens portion fusedJn the countersink and composed of a segment of different index of refraction having substantial edgethichiess and encompassed by at least two pieces of glass of substantially 20 the same-index of refraction as the major lens portion and fitting around and fused to the edge of the segment and substantially meeting so as to form a demarcation on each side of the segment to guide in the lateral disposition of the 25. optical center of the segment in the subsequentv 2. For multifocal lens blanks a minor lens portion for fusing in a countersink comprising a pieces of glass of a different index of refraction shaped and fused to the edge of the segment and substantially encompassing the same.

4. For multlfocal lens blanks a minor lens portion for fusing in a countersink comprising a segment of one index of refraction having a substantial edge thickness about its entire 'periphery and surrounded by glass of different index of refraction fused to the edge thereof and constituting a plurality of individual pieces.

5. For multifocal lens blanks a minor lens portion for fusing in a countersink comprising a segment of at least two pieces. of glass of different index of refraction fused edge to edge, and a .55 film amalgamated with the glass at the fused edges and constituting a li ht screen.

8. Ii'or multifocal lens blanks a minor lens portion for fusing in a countersink comprising an inner glass segment of relatively high index of refraction and a surrounding glass member of lower index fused to the segment edge to edge substantially about its entire periphery, and a film amgalgamated with the glass about the edge of the segment and constituting a light -'l. I'br multifocal lens blanks a minor lens portion for fusing in a countersink comprising a segment of one index of refraction. having substantial'edge thickness about its entire periphery and'two piecesof glass of a diilerent index of refraction fitting about and fused to the edge of thesegment with their proximate edges forming .lines of demarcation on opposite sides of the 1;,wasmmamalgamated h simianv lens portion of one index of refraction having a countersink in one face thereof, a minor lens portion fused in the countersink and composed of a segment of-diiferent index of refraction hav-' ing substantial edge thickness and encompassed by at least two pieces of glass of substantially the same index of refraction as the major lens portion and fitting around and fused to the edge of the segment and substantially meeting so as to form a demarcation on each side of the segment to uide in the'latteral disposition of the optical center of the segment in the subsequent grinding, and a film amalgamated withthe glass about the edge of the segment and constituting a light screen. e

9. A multifocal lens blank comprising a major lens portion of one index of refraction having a countersink in one face thereof, and a minor lens portion fused in the countersink and composed of a glass segment of a higher index of refraction having substantial edge thickness'and substantially surrounded by a two part glass member of substantially the same index of refraction as the major lens portion fused edge to edge to the segment with the proximate edges which consists in forming a countersink in a" of the two parts of the surrounding member forming lines of demarcation on opposite sides of the segment, and a film amalgamatedwith the glass about the edge of the segment and constituting a li ht creen. g

10. A multifocal lens blank comprising a major lens portion of one index of refraction having a sountersink in one face thereof, a minor lens portion fused in the countersink and composed of a segment of different index of refraction having substantial lateral edge thickness and flanked on each side by glass of substantially the same index of refraction as the mac! lens portion and edge fused to the segment, and perceptible substanttally radial lines on opposite sides of the segment for controlling the lateral disposition of the optical center of the segment in the subsequent grinding.

11. A multifocal lens blank comprising a major lens portion of one index of refraction having a countersink in one face thereof, a minor lens portion fused in the countersink and composed of a cut of different index of refraction having substantial edge thickness anden-, com by glass of substantially thesame index of refraction as the major lens portion and fitting around and fused to'the edge of the 888- ment, and perceptible'substantially on opposite sides of the segment for controlling the lateral disposition oi the optical center of the segment in the subsequent grinding.

12; Themethod of making a multifocal lens major lens portion, shaping a piece of glass ofdifierent index of refraction to the outline of the reading segment, grinding a plurality of pieces of glass of substantially the same'indexof refraction as the major lens to fit about the and together substantially to encompass it, edge fusing the encom glass pieces to the'segment to form a composite minor lens portion, and fusing the minor lens portion into the countersink.

' 13. The method of making a muitifocal lens whichconsistsinformingacountersinkina major lens portion, partially shaping a piece of glass of diiferent index of refraction to the outline of the reading segment, grinding a piece of 10 glass of substantially the same index of refraction as the major lens to fit about the shaped portion of the segment and edge fusing the two together, grinding the exposed peripheral portion of the segment and the adjacent edges of the surroundingglasspiecetoacontinuousedge,shapinga secondpieceofglassofthe sameindexofrefraction as the major lens to fit said continuous edge and fusing it thereto, thereby forming a compodte three part minor'lens, and fusingthe minor lens 20 inthe countersink. x 14. The method of making a multifocal lens blank in forming a countersink in a major lens blank, forming a minor lens blank by edge fusing about a t of relatively high in- 25 dex of refraction two glass members of the same index of refractionas the major lens blank en closingthesegmentandfonningattheirproxi-i mate edga a line of demarcation on each side of Y thet,fusingtheminorlensblankinthe30 countersink, and surfacing the face containing the minor lens blank to a continuous spherical curvature with the lines of demarcationof a predetermined relative length for the desired lateral disposition of the optical center of the segment. 15. A fused multifocal-lens having an internal shoulder constituting a boundary between two fields, the shoulder being formed by fusing pieces of glass having edges of substantial width, and the lens including a light absorptive film. applied to andincorporated in the shoulder forming theboundary between the two fields and rendering the edges substantially non-reflective, the film comw s s a d and a flux. V r

16. A fused multifocal lens having an internal shoulder constituting a boundary between two fields, the shoulder being formed by fusing pieces of glass having edges of substantial width, and the lens including a light-absorptive film applied to and incorporated in the shoulder forming the boundary between the-two fields and rendering the edgm non-reflective, the film comprising a bondingagent and a dye.

17..A fused multifocal lens having an internal shoulder constituting a boundary between two fields,thesho ulderbeingformedbyfusingpieces of glass having edgesofsubstantial width, and the lens including a light-absorptive film incorporated in the shoulder forming the nioundary betweenthetwofieldsandrenderingtheedg'essub GEQRGE A. CLEMENT. 

